1 Introduction

Giant cell tumor of the tendon sheath (GCTTS) is the second most common benign soft tissue tumor found in the hand, typically located along or within the tendon sheath.^1–8 GCTTS usually occurs in patients between the 3rd and 5th decade of life making it rare to find in the pediatric population.^8–10 The youngest known case at the time of this publication is in a 2-year-old involving the lower extremity.⁶ Here, we present a case of a 21-month-old female who was diagnosed with GCTTS of her index finger.

2 Case report

A 21-month-old female presented to the pediatric orthopaedic clinic after her mother noticed a non-tender mass on the palmar aspect of her index finger about a month prior to her appointment. She reported no known injury and no discomfort. Over the month prior, the mother noted a purple-bluish hue to the mass and acknowledged an increase in size since first appearance. The patient was born full term via a normal spontaneous vaginal delivery and had no other significant medical problems. On physical examination, there was a solitary mass approximately 1cm × 1.5cm located on the palmar ulnar aspect of the mid portion of the proximal phalanx of the index finger (Fig. 1). It appeared adherent to the skin, with a bluish hue which did not change with elevation or compression. It was nontender to palpation and nonmobile relative to the flexor tendon. She was neurovascularly intact to the digit.

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Fig. 1 Mass visible on finger. Volar index finger mass over the proximal phalanx of the index finger at preoperative visit.

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Plain radiographs revealed normal appearing bone without periosteal reaction (Fig. 2). Ultrasound demonstrated a multi-cystic lesion surrounding the flexor tendon (Fig. 3). Adjacent soft tissue swelling was also noted with low resistance arterial waveforms. On MRI T2 images a heterogenous subcutaneous soft tissue mass measuring 11mm in diameter was noted within the flexor tendon sheath with moderate diffuse enhancement with gadobutrol administration. There was slight surrounding edema but the mass did not extend deep to the tendon, nor did it invade the underlying bone (Fig. 4).

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Fig. 2 Radiographic findings. PA and lateral plain radiograph showing soft tissue swelling about the index finger without periosteal reaction or osseous changes.

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Fig. 3 Ultrasound of index finger mass. Arrowhead: proximal phalanx. Asterisk: Flexor tendon. Arrow: multilobulated cystic appearing lesion associated with flexor tendon and skin.

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Fig. 4 MRI imaging of mass. Fat suppression sagittal MRI post-contrast administration with moderate diffuse enhancement of the mass (left). Axial T2 image showing a heterogeneous mass extending down to the flexor sheath without bone involvement (right).

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A joint decision between the patient's guardian and surgeon was made to perform an excisional biopsy based on location of the mass, its noticeable increase in size from guardian's report, and the potential interference with hand function as the patient grew. A needle biopsy was not performed preoperatively based on the overall benign features of the lesion, the guardian's preference for complete excision with a single procedure regardless of the mass being benign or malignant. Preoperatively it was discussed with the guardian that based on the size of lesion and the location on the finger, there may be issues with skin closure that could necessitate a skin graft at the time of surgery. A volar approach with a Brunner style incision that spanned from the palmo-digital crease to the proximal interphalangeal crease, the incision did not cross flexion creases to avoid flexion contracture and scarring. Intraoperatively, we identified the mass extending from the flexor tendon sheath at the level of the A3 pulley. Given the non-critical function of the A3 pulley, a small portion was excised to ensure adequate removal of tumor. We resected the tumor with the assistance of magnification loupes and tissue samples were sent to pathology for analysis (Fig. 5). The tumor bed was cauterized with the bipolar and skin was closed after hemostasis was achieved. The patient was temporarily placed in a soft club cast for soft tissue protection given their age. Histopathology revealed multinodular proliferation with a mixture of large histiocytoid cells, smaller mononuclear cells and scattered multinucleated giant cells. There were areas of hyalinization and sclerosis as well as deposition of hemosiderin (Fig. 6). By immunohistochemistry, ERG and CD31 highlighted small vascular channels within the lesion but not the lesional cells. SMA was weakly positive, whereas desmin, SPA, pan-cytokeratin were negative. Most of the lesional cells were positive for D2-40. These features were most consistent with GCTTS. The patient had uncomplicated initial healing; at three years post op, the patient was pain-free without deficit and had no recurrence of the mass.

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Fig. 5 Gross surgical specimen. Surgical resection of the index finger mass and gross specimen of the heterogenous mass associated with the flexor sheath.

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Fig. 6 Histopathologic features of tenosynovial giant cell tumor. (A) The tumor is lobulated and well circumscribed, composed of an admixture of abundant histiocyte-like cells, few larger epithelioid cells, and scattered osteoclast-like giant cells (hematoxylin-eosin stain; original magnification ×100). (B) In some areas, the larger epithelioid cells and giant cells are prominent. Hemosiderin deposits are present (hematoxylin-eosin stain; original magnification ×400).

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Pediatric hand tumors in general are quite rare. While the differential for GCTTS must always include potential malignant conditions, the vast majority are benign. Other more common, benign soft tissue tumors in the pediatric population include ganglion cysts, hemangiomas, and fibromatous lesions.^15,16 Ganglion cysts are among the most commonly encountered pediatric hand masses and account for approximately 22–25 % of masses that are surgically removed in this population.^15,16 These benign masses are typically mucin-filled collections derived from an underlying joint space that fluctuate in size and can cause discomfort. They can occur in multiple locations including the dorsal wrist, volar wrist, and the flexor and extensor tendon sheaths.¹⁷ Shah et al. found approximately 50 % of ganglions in the pediatric hand to be on the dorsal wrist. However, patients 10 years and younger were more likely to have ganglions on the volar wrist and flexor sheath than older patients.¹⁸ Though typically unnecessary for diagnosis, MRI findings reveal a very well circumscribed cystic lesion. Vascular anomalies are another group of commonly encountered pediatric hand masses, 90 % of which are hemangiomas and vascular malformations.¹⁹ These masses can be seen anywhere on the upper extremity but often are on the forearm or dorsal aspect of the hand. Hemangiomas typically show initial proliferation followed by spontaneous involution completed by the age of 5–7 years; malformations typically grow proportionally with the patient. Depending on the specific type of lesion, vascular anomalies have multiple clinical presentations. Strawberry or bluish masses, compressible masses the refill, or those with a palpable bruit may be indicative of a vascular tumor. MRI is the imaging study of choice and will show a gadolinium enhancing mass with flow.^16,19 Fibromatous tumors comprise another category of hand mass found in the pediatric population. These masses are typically hard, painless masses that may cause deformity of the hand or display cutaneous involvement. Lesions may form anywhere on the hand but often form over the dorsum or lateral borders of the digits. These lesions are benign but can be locally aggressive. Histology reveals dense fibrous proliferation with the presence of inclusion bodies. As with any mass of unknown etiology, malignancy should always be considered; however, in the pediatric hand, malignancy is exceedingly rare accounting for approximately 1–2% of surgically addressed masses.^15,16 Fibrosarcoma is one of the most common malignant masses found in the pediatric hand though synovial sarcoma, melanoma, malignant schwannoma, parosteal sarcoma, and angiosarcoma have been described.^15,16,19

3 Differential diagnosis

•Ganglion cyst•Hemangiomas•Fibromatous lesions•Vascular malformations•Malignant soft tissue lesionso Fibrosarcomao Malignant schwannomao Synovial sarcomao Melanomao Parosteal Sarcomao Angiosarcoma

4 Discussion

Tenosynovial giant cell tumors (TGCT) are a broad class of typically benign neoplasms originating from synovial, bursal, or tenosynovial tissues and encompasses multiple forms including GCTTS, nodular tenosynovitis, and pigmented villonodular synovitis. TGCTs can be further defined as localized or diffuse types. Localized types are typically well circumscribed, solitary lesions, most often found in the digits, and are often of tenosynovial origin; diffuse types are typically locally aggressive lesions that are more likely to recur, most often found near large joints, and are often of synovial origin. TGCT primarily affects patients in the third through fifth decades of life.^11,12 Incidence of localized TGCT ranges from 9 to 30 per million person-years and that of diffuse TGCT ranges from 2 to 8 million per person-years.^13,14 Specifically stratifying for localized TGCT in the digits, a Dutch study showed an incidence of approximately 34 million per person-years.¹⁴

GCTTS is exceedingly rare in the pediatric age group and prior to this presentation, the youngest known case report of GCTTS was a 2-year-old child and that involved the second toe.⁶ The largest retrospective single series in children only included 29 patients over a 16-year period with a mean age of 11. Highlighting the rarity of diagnosis in our patients' age group. Our patient's presentation was similar to the other children described in the respective case reports along with the patients described in the literature with GCTTS.^1–6 Of patients in the Ghove et al. case series, 96 % presented with physical examination findings of a firm and enlarging palpable, non-fluctuant soft tissue mass, similar to our patient.⁶ On plain radiographs, 48 % demonstrated soft tissue edema and none of the patients showed any bony erosion or calcification. On T2-weighted MRI, 14 of the 21 patients with MRI showed intermediate-to-high signal intensity with mild-to-moderate enhancement after administration of contrast. Previous histologic analysis has shown sheets of mononuclear histolytic cells with scattered giant cells and hemosiderin-laden macrophages, similar to our findings. Finding of the examination, image reports and histology were all consistent with the classic presentation of GCTTS and the presentation of our 21-month-old patient.

Pediatric hand tumors in general are quite rare. While the differential for GCTTS must always include potential malignant conditions, the vast majority are benign. Other more common, benign soft tissue tumors in the pediatric population include ganglion cysts, hemangiomas, and fibromatous lesions.^15,16 Ganglion cysts are among the most commonly encountered pediatric hand masses and account for approximately 22–25 % of masses that are surgically removed in this population.^15,16 These benign masses are typically mucin-filled collections derived from an underlying joint space that fluctuate in size and can cause discomfort. They can occur in multiple locations including the dorsal wrist, volar wrist, and the flexor and extensor tendon sheaths.¹⁷ Shah et al. found approximately 50 % of ganglions in the pediatric hand to be on the dorsal wrist. However, patients 10 years and younger were more likely to have ganglions on the volar wrist and flexor sheath than older patients.¹⁸ Though typically unnecessary for diagnosis, MRI findings reveal a very well circumscribed cystic lesion. Vascular anomalies are another group of commonly encountered pediatric hand masses, 90 % of which are hemangiomas and vascular malformations.¹⁹ These masses can be seen anywhere on the upper extremity but often are on the forearm or dorsal aspect of the hand. Hemangiomas typically show initial proliferation followed by spontaneous involution completed by the age of 5–7 years; malformations typically grow proportionally with the patient. Depending on the specific type of lesion, vascular anomalies have multiple clinical presentations. Strawberry or bluish masses, compressible masses the refill, or those with a palpable bruit may be indicative of a vascular tumor. MRI is the imaging study of choice and will show a gadolinium enhancing mass with flow.^16,19 Fibromatous tumors comprise another category of hand mass found in the pediatric population. These masses are typically hard, painless masses that may cause deformity of the hand or display cutaneous involvement. Lesions may form anywhere on the hand but often form over the dorsum or lateral borders of the digits. These lesions are benign but can be locally aggressive. Histology reveals dense fibrous proliferation with the presence of inclusion bodies. As with any mass of unknown etiology, malignancy should always be considered; however, in the pediatric hand, malignancy is exceedingly rare accounting for approximately 1–2% of surgically addressed masses.^15,16 Fibrosarcoma is one of the most common malignant masses found in the pediatric hand though synovial sarcoma, melanoma, malignant schwannoma, parosteal sarcoma, and angiosarcoma have been described.^15,16,19

In adults, recurrence rates of GCTTS range between 10 and 44 %.^7–10 Known risks for recurrence include location at distal interphalangeal joint of finger, osseous pressure erosion, mitotic activity on histology, proximity to arthritic joint, tumor gene nm 23 and Al-Qattan type II tumors.²⁰ Age at presentation did not appear to be a risk factor; however, poor surgical technique with incomplete excision was also a primary risk factor. Excision with magnification equipment resulted in the lowest recurrence rate. Children, especially under the age of two, have much smaller anatomical structures compared to adults, making excision of pathology challenging. Nonetheless, Gholve et al. demonstrated a 0 % recurrence rate among all 29 pediatric cases with everyone having at least a 1-year follow up and the majority having a 2-year follow up appointment.⁶ Highlighted by this study is the lack of long-term outcomes in pediatric patients and frequently patients and parents are concerned with the possibility of recurrence beyond 2 years or over their lifetime. Our patient's mass was located over the mid portion of the proximal phalanx, had no osseous involvement or erosion, was not near an arthritic joint and was resected with assistance of magnification equipment. Together, these features give us confidence that it has a low chance of recurrence at least within the first 1–2 years post-operatively.

5 Conclusion

Although extremely rare in the pediatric population, GCTTS should be included on the differential in patients under ten years of age. GCTTS can be difficult to completely excise as the mass can locally invasice; the relatively small anatomy of pediatric patients makes excision challenging, and we encourage loupe magnification for identification and protection of the neurovascular bundle. Presenting symptoms, images, and histology in children is consistent with adults. The current literature on GCTTS excludes young children similar to our patient and it is important to recognize that this pathology can affect children of all ages. Children can have a successful outcome after excision of GCTTS if meticulous dissection and complete resection is obtained although no long-term outcomes have been reported, making patient counseling difficult.

Conflict of interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:JM reports a relationship with BoneSupport that includes: consulting or advisory. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Financial support and sponsorship

N/A.

Informed consent

Informed consent was obtained from the family of this patient to discuss this case without disclosing identifiable information.

Ethical statment

This study did not involve human, or animal research submits. The ethical principles of research writing were followed in creation and completion of this case report and manuscript.

Funding statment

There was no financial support or funding sources that contributed to the completion of this case report and manuscript.

Statement of informed consent

Informed consent was obtained from the family of this patient to discuss this case without disclosing identifiable information.

CRediT authorship contribution statement

Blaire McCarthy: Investigation, Writing – original draft, Data curation, Writing – review & editing. Joseph Romano: Investigation, Writing – original draft, Writing – review & editing. Jonathon Yu: Conceptualization, Writing – review & editing. Jed I. Maslow: Conceptualization, Methodology, Writing – review & editing.